Impact of Tritrichomonas spp. on the immune system of Muc2^–/– mice after antibiotic therapy

While pathogenic protists inhabiting the reproductive tract are well studied, the gastrointestinal (GI) tract contains a constitutive protist microbiota that is an integral part of the vertebrate microbiome. Currently, the effect of protozoan infections on the host immune system and their potential contribution to disruption of mucosal immune homeostasis are not well understood. Protists, along with bacteria and viruses, are permanent representatives of the human microbiota. The main attention of researchers is focused on studying their pathogenic role in gastrointestinal diseases. However, their role in symbiotic relationships with hosts is relatively little studied. It was previously shown that the closest human ortholog of mouse Trichomonas (Tritrichomonas spp.) is Trichomonas Dientamoeba fragilis, which can cause symptoms of inflammatory bowel disease. It is currently unclear whether Dientamoeba fragilis and other protist species such as Enteromonas spp., Entamoeba dispar are commensals, pathobionts, or pathogens of the human intestinal tract. Thus, information about the mutualistic relationships between protists, the gastrointestinal microbiota, and the immune system of mice can be used to understand host-protozoan relationships in humans. The data obtained allow us to evaluate the potential contribution of commensal protozoa in the formation of protective mechanisms of the mucous membrane of animals and humans. We have previously shown that antibiotic therapy leads to an increase in the number of Tritrichomonas spp. along with a reduction in bacteria in the gut of mice with a mutation in the Muc2 gene. A mutation in this gene leads to impaired formation of the intestinal mucosa in mice. Mice with a mutation in the Muc2 gene can be used as model to study human inflammatory bowel diseases (IBDs). In this work, we conducted a comparative study of the immunological status of Muc2^–/– mice harboring Tritrichomonas spp. after antibiotic therapy for 2 weeks followed by gavage of Lactobacillus johnsonii into mice and mice without introduction of probiotic microorganisms (self-recovery). Analysis of the main populations of lymphocytes in the blood, spleen and lymph nodes showed that the introduction of Lactobacillus johnsonii after antibiotic therapy leads to a significant increase in the population of T-lymphocytes in the blood and spleen, and an increase in the number of helper T cells in the lymph nodes of Muc2^–/– mice compared to mice without the addition of probiotic microorganisms.